Re: Detecting whether UV fits into an NV

[stevieb]

"It annoys me that I can't find a way to detect and shift all of the trailing zero bits off in one hit - and that I instead have to detect and shift them off one at a time. "

Depending what platform you're on, check if the __builtin_ctz() function is available to you. The ctz stands for 'count trailing zeros'. Use this to get the number of trailing zeros, then shift them all off at once.

Update: I've added in bitCount(), which allows you to send in the number after stripping off the trailing zeros, and returns a count of the remaining bits.

#include <stdio.h>
#include <math.h>

unsigned int bitCount(int num);

void main () {

    /* Here's your example number, in binary format for visual purpose
+s */

    int num = 0b10100000;

    int noTrailingZeros = num >> __builtin_ctz(num);
   
    unsigned int bitsRemain = bitCount(noTrailingZeros);

    printf(
        "Zeros: %d, No Zeros: %d, Bits remain: %d\n", 
        num, 
        noTrailingZeros, 
        bitsRemain
    );
}

unsigned int bitCount(int num) {
    unsigned int bits = 0;

    while (num) {
        bits++;
        num >>= 1;
    }

    return bits;
}

Output:

Zeros: 640, No Zeros: 5, Bits remain: 3